The usual injection molding device is generally composed of a fixed plate and a movable plate bearing respectively the two halves of a mold, with a third fixed plate forming a support or bed, All three plates are vertically disposed. Four parallel, horizontal columns make the bed integral with the fixed plate and guide the movable plate during its travel between the fixed plate and the bed under the action of hydraulic jacks, which also lock the two halves of the mold together.
In such known molding devices the columns traverse the fixed plates which they connect outside the zone occupied by the mold. These columns are also spaced as far as possible one from the other to enable access to the molding zone, generally being situated at the four corners of the plates. With such an arrangement the distribution of the forces transmitted by the plates to the columns is uneven at the level of the plates, however, whether in horizontal or vertical directions. In addition, as the plates must not undergo any deformation, it is necessary for them to have very high resistance to be able to withstand this poor force distribution. Also, as the columns join the plates outside the zone occupied by the mold, the dimensions of the plates are much greater than those of the mold itself. The result is that the plates have to be of a higher weight and therefore are more costly to produce.
In addition, when the object to be molded has relatively large dimensions, the injection and locking forces are large. As the columns have to bear these large forces they have to be of a relatively large diameter, and are therefore very difficult and costly to manufacture. Further, since the columns also guide the movable plate, when binding occurs during sliding, it is necessary to access the columns and disassemble them.